1. Field of the Invention
The present invention relates to a waterproof rubber sheet. More particularly, the present invention relates to a waterproof rubber sheet comprising ethylene-.alpha.-olefin rubbers which are useful in the waterproofing of buildings or the water-tightening of water reservoirs, irrigation canals and the like.
2. Description of the Related Art
Since an ethylene-.alpha.-olefin rubber has good heat resistance, weather resistance, ozone resistance, cold resistance and chemical resistance, it is widely used in the waterproofing sheet fields, for example, waterproofing of building roofs, the water-tightening of rivers, ponds, irrigation canals or the prevention of pollution of ground water with harmful substances which are liberated from industrial wastes.
In waterproofing sheet fields, sophisticated adhesion techniques are required. Since the ethylene-.alpha.-olefin rubber is a non-polar rubber, its adhesion is more difficult than other rubbers such as natural rubbers, styrene-butadiene rubbers, butyl rubbers, chloroprene rubbers, chlorosulfonated polyethylene and the like.
Since an adhesive used for adhesion is generally of the organic solvent type, it has various problems in that it is flammable or dangerous for users' health or its adhesion force is greatly influenced by environmental conditions after the application of the adhesive (e.g. weather, climate, temperature, keeping time, etc.). Because of such a situation, a fusion bondable waterproof sheet attracts attention.
As the fusion bondable waterproof sheet, a polyvinyl chloride sheet and a thermoplastic elastomer sheet are well-known. The fusion bondable waterproof sheet is adhered to a substrate by melting the sheet by heating, contact bonding the sheet to the substrate and cooling to solidify the sheet. In the case of the rubber sheet, since the rubber is crosslinked, the sheet cannot be molten and deformed so that fusion bonding of the rubber sheet is said to be difficult.
To fusion bond the crosslinked rubber sheet, a thermoplastic resin layer is inserted as a fusion bondable layer between the crosslinked rubber sheets. However, the resin has drawbacks such as poor flexibility, and elongation and contraction due to temperature change according to the seasons. In addition, it is a big problem in the production of practical products to composite the thermoplastic resin as the fusing bondable layer with a part of the crosslinked rubber sheet. Therefore, a the fusion bondable waterproof rubber sheet is not generally used.
Japanese Patent Application No. 99416/1987 discloses a method for producing a waterproof sheet by fusion bonding an uncrosslinked sheet to a substrate and then crosslinking the sheet at room temperature. However, since the fusion bonding is carried out in a place where the waterproof is laid, there are various problems such that it is difficult to prevent crosslinking of the sheet in a variable period from the production of the uncrosslinked sheet to the waterproof laying, and that the crosslinking rate is low at room temperature or that the rubber sheet has small strength during application, so that breakage, waviness due to plastic deformation, size change, or deformation and self adhesion occur during storage.